912
LETTERS TO THE EDITOR
RANGE OF NITROGEN AND BERYLLIUM
IONS IN AIR
Iu. A. VOROB' EV
Ion
vx
J. Exptl. Theoret. Phys. (U.S.S.R.) 35, 1306-1307
(November, 1958)
WE measured the range of nitrogen and beryllium
ions in air in the velocity interval form 8 x 10 8
em/sec to 11.5 x 10 8 em/sec, using a cloud chamber filled with a mixture of air and water vapor
under a pressure of 15 em Hg before expansion.
The Ntl. NU, Nt53 , and Bet2 ions, accelerated
by a 72 em cyclotron, were bent by a focusing magnet and, after traversing a celluloid film 35 to 40
JJ. g em - 2 thick, entered into the working volume of
the cloud chamber. An electrostatic deflection
scheme was used, activated by the governing system of the cloud chamber to ensure the entrance
of the particles into the chamber at the exact instant of expansion.
The ion velocity was determined from laboratory data on the calibration of the focusing magnet,
expressed in terms of the dependence of ME/Z 2
on I (M, E and Z are the mass, energy and
charge of the ion, I is the current in the coils
of the focusing magnet). The error in the velocity
determination did not exceed ± 3%.
Ions of molecular deuterium D{ were accelerated in addition to nitrogen and beryllium. Comparison of the ranges of nitrogen and beryllium
ions with the range of deuterons obtained from
the decay of molecular deuterium ions allows the
determination of the ranges of nitrogen and beryllium in air under normal pressure. The range of
deuterons in air under normal pressure was determined from the range-energy relations in
Segre's book. 1 The air equivalent of the film was
taken to be 0.045 em in agreement with the data
on a particles. 2 The error in the determination
of the range of nitrogen and beryllium ions does
not exceed ± 5% and is due, mainly, to straggling
in the range of deuterons and of the ions under
study. The measured values of the range in air
of the N14, N15• and Be 9 ions are given in the
table.
em/sec
Rair' em
Moscow State University
Submitted to JETP editor July 26, 1958
to-•
Be,
N,.
8.2
9.0
10.2
11.4
8.1
8.2
8.9
0.66
0.78
0.88
1.13
0.69
0. 78
0.85
The results for Ntl and NU are in good agreement with the data of Reynolds and Zucker 3 on the
range of N14 in the photoemulsion, if the emulsion
stopping power is assumed to be the same for nitrogen ions and a particles of equal initial velocities.
An estimate of the ranges by the Knipp and Teller
method for y = 1.15 (y is the ratio of electron to
ion velocities at which capture and loss of a given
electron have equal probabilities) shows that the
range of Be 9 ions at v = 8.5 x 10 8 em/sec should
be smaller by about 10% than the range of N14 ions
with the same initial velocity.
The measured ranges of Be 9 ions at v = 8.2
and 8.9 x 10 8 em/sec exceed the corresponding
ranges for N14 ions by 12 to 15%. This discrepancy is apparently explained by a peculiarity in
the electronic shell structure of the beryllium
atom whose successive ionization potentials are
9.3, 18.1, 153 and 216 v (the corresponding
values for nitrogen are 14.9, 29.4, 47.4, and
77.0 v). Due to the strong binding of the K
electrons the beryllium ions will have an anomalously low effective charge through a considerable
part of their range, which explains the increase in
the range.
I wish to express my gratitude to the cyclotron
crew consisting of Engineer-Physicist G. V.
Kosheliaev and operators A. A. Danilov, V. P.
Khlapov and M. S. Merkulov for their part in the
completion of this work.
1 E. Segre, editor, Experimental Nuclear Physics
(Russ. Transl.), vol. 1, M. IlL, 1955.
2 Barile, Webeler, and Allen, Phys. Rev. 96, 673
(1954).
3 H.
L. Reynolds and A. Zucker, Phys. Rev. 96,
393 (1954).
4 J. Knipp and E. Teller, Phys. Rev. 59, 659
(1941).
Translated by A. M. Bincer
280